Method of lapping dies



Nov. 6, 1934. w. E. HOKE 1,979,689

- METHOD OF LAPPING DIES Filed Feb. 27, 1951 Patented Nov. 6, 1934 1,979,689 METHOD OF LAPPING DIES William E. Hoke, Baltimore, Md., assignor to Dardelet Threadlock Corporation, New York,

N. Y., a corporation of Delaware Application February 27,1931, Serial No. 518,784

7' Claims.

Important objects of the present invention are, to provide for better lapping of thread-forming dies and chasers and other toothed articles; to provide for improved high precision lapping of thread-forming dies,. chasers and the like; to provide for improved lapping of thread-forming dies and chasers by a lapping operation upon the crest surfaces of the die or chaser teeth and a separate lapping operation upon the side faces m of the teeth; to provide for thorough lapping of the crest surfaces and side faces of the teeth without rounding the tooth corners; and to provide for improved lapping of dies or chasers which are designed for forming a self-locking screw thread of well known type having an inclined locking surface and converging side faces.

In the drawing, Fig. 1 is a plan view showing a die operatively disposed upon one of the lapping plates;

Fig. 2 an enlarged fragmentary perspective view of the die;

Fig. 3 an enlarged fragmentary perspective view of the lapping plate for lapping the crest surfaces of the die teeth;

Fig. 4 an enlarged fragmentary perspective view of the lapping plate for lapping the side faces of the die teeth;

Figs. 5 and 6 detail sectional views showing th manner of preparing the laps;

Fig. 7 an enlarged detail sectional view showing the lapping of the crest surfaces of the teeth;

Fig. 8 an enlarged detail sectional view showing the lapping of the faces of the teeth; and

Fig. 9 an enlarged detail sectional view showing the thread-forming operation of the die upon a bolt shank.

The. drawing illustrates the lapping of a thread-forming rolling die in accordance with my invention. It will be understood however that the invention is applicable to chasers and numerous other toothed articles requiring accurate lapping. The rolling die, designated 1, is of flat, rack form. Its teeth or ribs are obliquely disposed upon the working face of the die at an angle in accordance with the pitch angle of the thread to be formed. In cross section the teeth are shaped for forming a well known self-locking thread of the type disclosed in U. S. Patent No. 1,657,244. Such a thread when it occurs upon a bolt or other male threaded member has an inclined root surface which makes an angle to the thread axis within the angle of friction and is to frictionally lock the thread-coupled members against unscrewing. The thread grooves are of greater width than the thread ribs and when the nut is turned without axial advance, as when tightening it, the threads are relatively displaced 0 crosswise of each other to bring the inclined crest and root surfaces into frictional locking engagement. Such threads, in their commercial form, usually have their side faces converging outward to form a taper whose included angle is twenty-nine degrees. The angle of the inclined locking surfaces to the thread axis is usually six degrees.

To form a bolt thread of the type described the die teeth 2 have their side faces 3 inclined similarly to the thread faces; 'the width of the teeth is the width of the thread groove; the crest surfaces 4 of the teeth are inclined six degrees for forming the self-locking root surfaces of the bolt, and the root surfaces 5 of the teeth are flat. die is preferably formed of tool steel, or the like, and the teeth are machined.

Two specially designed lapping plates 6 and '7 are employed successively for lapping the die teeth. Each plate is preferably rectangular and about twice as long as the die and twice as wide. Plate 6 is designed for lapping the inclined crest surfaces. For this purpose its working face is formed with a series of straight longitudinally extending lapping surfaces 8 which are flat and inclined to the same degree as the crest surfaces 4 of the die teeth (six degrees in the present instance). Said lapping surfaces are stepped successively in ratchet arrangement. The width of each is substantially equal to the pitch of the die teeth and each surface is connected to the next by an abrupt, fiat, shallow surface 9 which preferably makes an angle of fourteen and onehalf degrees with the general plane of the lap face. Surfaces 9 are all of equal depth so that the corrugations defined by surfaces 8 and 9 lie in the same general plane.

Lapping plate 7 is of rack form and is designed for lapping the side faces of the die teeth 2. Upon its working face the plate is formed with longitudinally straight ribs or teeth 10. These teeth. of materially greater depth than the die teeth 2, have flat side faces 11 converging to the same degree as the faces of teeth 2 and are proportioned and spaced to mesh with teeth 2. Their crest faces 12 and root faces 13 are flat and un-inclined.

Each lap is prepared by a high precision method wherein a series of similar laps are formed by machining or otherwise, or selected, and different laps of the series are placed together in pairs The and in a particular sequence and operated for mutual lapping, with a suitable non-charging abrasive. Fig. 5 shows a pair of the laps 7 meshed for mutual lapping, and Fig. 6 shows a pair of the laps 6 meshed for mutual lapping. For example, assume that a series of three of the laps 7 are formed and designated A, B and G. Then, one cycle of lapping operations may be performed by lapping together first A and B, next A and C and then B and C. In a third cycle A and C, C and B and A and B may be successively lapped together. The cycles may be repeated .as often as required and preferably the laps will be repeatedly reversed endwise. The symmetrical form of the teeth 10 permits this reversal. By this repeated interchange, reversal and mutual lapping, errors are distributed and evened throughout the series of laps, and laps of the highest precision are produced. The laps are straightened, their tooth pitch is evened and their lapping surfaces are properly prepared. The lap 6 is prepared in a similar manner by mutual, sequential lapping with similar laps of a series. The corrugations of lap 6 however will not permit the reversal of the lap as in the case of lap 7. However its shallow corrugations are of a form to permit a limited transverse lapping movement upon a companion lap, in addition to the longitudinal lapping reciprocation.

The high precision lapping racks 6 and '7 are employed in succession for lapping the teeth of the die, with the use of a suitable charging abrasive. Preferably the crest surfaces 4 of the die are first lapped by placing the die upon lap 6 with the crest surfaces 4 in contact with the similarly inclined and wider lapping surfaces 8 as indicated in Fig. 7. The dieis then relatively reciprocated longitudinally upon the lap either manually or mechanically and preferably under a yielding pressure. For increased lapping effect the die may also be given a limited relative lateral movement which is permitted by the width of the lapping surfaces 8. The lap contacts the crest surfaces only of the die teeth, and the abrasive material is free to escape laterally past the crest corners of the profile of the teeth. Thereby crowding of the abrasive material and consequent rounding of the tooth corners is prevented. In the course of the lapping operation the die may be laterally shifted to different positions upon the wider lap, to bring different crest surfaces and lapping surfaces into contact.

For lapping the side faces 3 of the die teeth, the die is placed upon lap '7, with the teeth 2 of the die in mesh with the teeth 10 of this lap, and the crests 12 of the teeth 10 contacting, if possible, with the root surfaces 5 of the die teeth, as indicated in Fig. 8. Then, the die is relatively reciprocated upon the lap either manually or mechanically, and preferably under yielding pressure. In the course of the lapping operation the die may be repeatedly reversed endwise upon the lap and may be laterally shifted to different positions upon the wider lap to bring different teeth into mesh for better lapping effect. The symmetrical, high precision lapping teeth 10 accurately lap the side faces of the die teeth, even up the pitch of the die teeth and lap the root surfaces 5 of the die teeth.

It will be observed that during this face-lapping operation there is no lapping action upon the crests a of the die teeth. This is an important feature. Due to the greater depth of the lapping teeth 10 the root surfaces thereof are spaced materially away from the crest surfaces 5 of the are left unimpaired.

die teeth. It is impossible to lap internal corners such as are formed at the roots of the lap teeth without forming a fillet which would in turn round the corners of the die teeth. By elongating the lap teeth and forming them so that their side faces extend materially past the crest surfaces of It is preferable to first lap the crests of the die teeth and next the side faces of the teeth as described, for the reason that in the use of the crest lap 6the shallow surfaces 9 may have an undesired lapping effect upon the tooth faces, and subsequent use of the face lap 7 will correct this effect. However, with the exercise of reasonable care in crest-lapping said effect may be prevented and the crest-lapping and face-lapping operations may be safely performed in reversed order. It is also possible that the operations will be alternated in the course of preparing the die. Regardless of the sequence, the die will be prepared for forming a more precisely accurate self-locking thread with an even pitch, accurately inclined locking surface, smooth faces and no rounded corners at the junctures of the inclined locking surface with the side faces of the thread.

What I claim is:

1. The method of lapping a toothed or ribbed thread-forming die or chaser having teeth with transversely inclined crest surfaces by separate operations to prevent blunting of the crest corners of the teeth, consisting in lapping the side faces of the die teeth and evening the pitch of the teeth by meshing them with deeper teeth of a lap and causing relative lapping movement between the die and lap with the lap held out of contact with the crest surfaces of the die teeth 12 by the greater depth of the lap teeth and .with abrasive material free to escape along the depth of the lap teeth past the crest corners of the profile of the die teeth; and lapping the said crest surfaces only by engaging the die with a lap having lapping surfaces inclined similarly to the crest surfaces of the die teeth and formed and disposed for lapping the said crest surfaces while permitting free escape of abrasive material laterally past the crest corners of the profile of the die teeth.

2.- The method of producing an accurately lapped,- toothed or ribbed thread-forming die or chaser, consisting in preparing a high precision toothed lap having teeth of greater depth than the die teeth, by repeated interchanging and mutual lapping with other similar laps; meshing the die teeth with the teeth of the prepared lap and causing relative lapping movement between the meshed die and lap for lapping the side faces of the die teeth and evening the pitch of the die teeth with the lap held out of contact with the crest surfaces of the die teeth by the greater depth of the lap teeth and with abrasive material free to escape along the depth of the lap teeth past the crest corners of the profile of the die teeth; and engaging the die with another high precision lap formed for lapping the crests of the die teeth and prepared similarly to said toothed lap and causing relative lapping movement between the die and said crestlap to lap the crests only while permitting free escape of abrasive material laterally past the crest comers of the profile of the die teeth.

3. The method of lapping a thread-rolling die plate having relatively wide, longitudinally straight ribs or teeth separated by narrow grooves and tapering outward and formed with transversely inclined flat crest surfaces, consisting in lapping said crest surfaces only by engaging them with fiat, longitudinally straight lapping surfaces of greater width than said crest surfaces and inclined similarly to the latter and carried by a lappingplate, and causing relative longitudinal reciprocation between said die and lap while permiting free escape of abrasive material laterally past the crest corners of the profile of the die teeth; and lapping the side faces of the tapered die teeth and evening the pitch of the teeth by meshing them with similarly tapered materially deeper and longitudinally straight teeth formed upon another lapping plate, and causing relative lapping reciprocation between the die and said lap longitudinally of the teeth under yielding pressure with the lap held out of contact with the crest surfaces of the die teeth by the greater depth of the lap teeth and with abrasive material free to escape along the depth of the lap-teeth past the crest corners of the profile of the die teeth.

4. The method of lapping an article of rack form having tapered teeth with inclined crest surfaces, consisting in lapping the side faces of the article teeth and evening the pitch of the teeth by meshing them with deeper tapered teeth of a lap of rack form and relatively reciprocating the meshed article and rack under pressure for lapping, with the lap held out of contact with the crest surfaces of the article teeth by the greater depth of the lap teeth and with abrasive material free to escape along the depth of the lap teeth past the crest corners of the profile of the article teeth; and engaging the crests only of the article teeth with another lap having inclined lapping surfaces for engaging the inclined crests, and relatively reciprocating the article and lap while permitting free escape of abrasive material laterally past the crest corners of the profile of the article teeth.

5. The method of lapping an article having rack teeth, consisting in lapping the faces of the teeth by meshing them with deeper teeth of a lap, and causing relative lapping movement between the meshed article and lap with the lap held out of contact with the crest surfaces of the article teeth by the greater depth of the lap teeth and with abrasive material free to escape along the depth of the lap teeth past the crest corners of the profile of the rack teeth.

6. The method of lapping atoothed article consisting in lapping the faces of the teeth and evening the tooth pitch by closely meshing the teeth with tapered deeper teeth of a lap, and causing relative lapping movement between the toothed article and lap to even the tooth pitch by simultaneous lapping effect of both opposite faces of the lap teeth, with the lap held out of contact with the crest surfaces of the article teeth by the greater depth of the lap teeth and with abrasive material free to escape along the depth'of the lap teeth past the crest comers of the profile of the article teeth.

7. The method of lapping a toothed or ribbed article by separate operations to prevent blunting of the crest corners of the profile of the teeth, comprising lapping the side faces of the teeth and evening the tooth pitch by one operation while avoiding lapping of the crests of the teeth and while permitting free escape of abrasive material depthwise of the teeth past the crest corners of their profile; and lapping the crests only of the teeth by another operation while permitting free lateral escape of abrasive material past the crest 

